This research is directed toward gaining an understanding of the mechanism of the biological effects of carcinogens and/or mutagens. Our approach is multi-disciplinary and involves (1) identifying and quantitating the chemical reactions occuring when DNA is treated in vitro or in cells with the powerful carcinogen ethylnitrosourea, as contrasted to less carcinogenic alkylating agents, (2) studying the chemical properties of the O-alkyl derivating from ethylnitrosourea reaction and (3) studying the coding or base-pairing properties of O-alkyl derivatives when they are incorporated into codons or polynucleotides.